In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed.
For example, one parameter in providing good performance and capacity for a given communications protocol in a communications network is the ability to provide efficient network access for wireless devices served by the communications network.
In general terms, in order for a wireless device to establish network access it, according to the Long Term Evolution (LTE) family of telecommunications standards, initiates a random access procedure. In a first step the wireless device transmits a random access preamble to the network node in the communications network. The network node responds with a random access response. This is followed by a scheduled transmission from the wireless device and a contention resolution by the network node. Properties in relation to the random access response in LTE will be disclosed next.
Once the random access preamble is transmitted and regardless of the possible occurrence of a measurement gap or sidelink discovery gap for reception, the wireless device monitors a Physical Downlink Control Channel (PDCCH), such as the MPDCCH, where the M stand form machine type communications, for random access response(s) identified by the random access Radio Network Temporary Identifier (RA-RNTI) in the random access response window which starts at the subframe that contains the end of the preamble transmission plus three subframes and has a length in terms of subframes defined by a parameter denoted ra-ResponseWindowSize-r3.
Once a radio resource control (RRC) connection request message (also sometimes known as Message 3, or MSG3 for short), is transmitted from the wireless device, the medium access control (MAC) entity in the wireless device starts a timer denoted mac-ContentionResolutionTimer-r13 and restarts the mac-ContentionResolutionTimer-r13 at each hybrid automatic repeat request (HARQ) retransmission.
According to the document 3GPP TS 36.213 version V13.1.1, for the protocol layer 1 (L1) random access procedure the uplink transmission of a Bandwidth reduced Low complexity (BL) device or a Coverage Enhancement (CE) device after a random access preamble transmission is as follows.
If a PDCCH with associated RA-RNTI is detected and the corresponding Downlink Shared Channel (DL-SCH) transport block reception ending in subframe n contains a response to the transmitted preamble sequence, the wireless device, according to the information in the response, transmits an UL-SCH transport block in the first subframe n+k1, where k1≥6, if the uplink delay field in subclause 6.2 of 3GPP TS 36.213 version V13.1.1 is set to zero where the subframe n+k1 is the first available uplink subframe for Physical Uplink Shared Channel (PUSCH) transmission, where for time division duplex (TDD) serving cell, the first uplink subframe for PUSCH transmission is determined based on the uplink/downlink configuration (i.e., as given by a parameter denoted subframeAssignment) indicated by higher protocol layers. The subframe n+k1 is the first available uplink subframe for PUSCH transmission determined based on a parameter denoted fdd-UplinkSubframeBitmapLC for frequency division duplex (FDD) and parameters denoted fdd-DownlinkOrTddSubframeBitmapLC and subframeAssignment for TDD. The wireless device postpones the PUSCH transmission to the next available UL subframe after n+k1+Δ, if the field is set to 1. The value of Δ is the number of RRC connection request message PUSCH repetitions as indicated in the random access response.
If a random access response is received and its reception ends in subframe n, and the corresponding DL-SCH transport block does not contain a response to the transmitted preamble sequence, the wireless device will, if requested by higher layers, be ready to transmit a new preamble sequence no later than in subframe n+5.
If no random access response is received in subframe n, where subframe n is the last subframe of the random access response window, the wireless device will, if requested by higher layers, be ready to transmit a new preamble sequence no later than in subframe n+4.
For Type2-MPDCCH common search space, the number of physical resource block (PRB)-pairs in MPDCCH-PRB-set P is 2+4 PRB-pairs.
If the most recent coverage enhancement level used for PRACH (Physical Random Access Channel) is coverage enhancement level 0 and 1, the aggregation and repetition levels defining the search spaces and the number of monitored MPDCCH candidates are determined from Table 9.1.5-1b in 3GPP TS 36.213 version V13.1.1, by assuming that the number of candidates for L′<8 as zero.
If the most recent coverage enhancement level used for PRACH is coverage enhancement level 2 and 3, the aggregation and repetition levels defining the search spaces and the number of monitored MPDCCH candidates are determined from Table 9.1.5-2b in 3GPP TS 36.213 version V13.1.1, where r1, r2, r3, r4 are determined from Table 9.1.5-3 in 3GPP TS 36.213 version V13.1.1 by substituting the value of rmax with the value of higher layer parameter mPDCCH-NumRepetition-RA.
However, there is still a need for an improved random access procedure for the wireless device.